This invention relates to a portable machine tool.
The Model BB1149 Portable Boring Bar sold by Climax Portable Machine Tools, Inc. of Newberg, Oregon is a portable boring machine that is used for boring out a hole in a workpiece to a desired diameter and with its axis at a desired orientation. Referring to FIG. 1 of the drawings, spacer plates 4A and 4B are tack welded to opposite sides of the workpiece (not shown) and mounting brackets 8A and 8B are attached to the spacer plates respectively using screws. Each mounting bracket includes a ring portion that defines a circular aperture. The manner in which the mounting brackets are attached to the spacer plates allows movement of the mounting brackets relative to the spacer plates, and the mounting brackets are initially positioned so that the centers of the two circular apertures lie at least approximately on the desired central axis of the final bore. A mounting bearing 12 is attached to each mounting bracket in a manner allowing limited movement of the mounting bearing relative to the mounting bracket. The assembly of the mounting bearing and mounting bracket may be as shown in U.S. Pat. No. 4,990,037, the disclosure of which is hereby incorporated by reference herein. As shown in U.S. Pat. No. 4,990,037, the mounting bearing is generally cylindrical, having a central axis, and defines a passage through which an elongate boring bar extends with clearance. A collar defines a bore through which the boring bar extends with a snug fit allowing rotational and axial relative movement, and a spherical bearing is effective between the collar and the mounting bearing and allows the collar to pivot relative to the mounting bearing about a point that lies on the central axis of the mounting bearing. The mounting bearing has a spherical external bearing surface, and the center of curvature of the spherical bearing surface coincides with the center of pivotal movement of the collar relative to the mounting bearing.
Referring again to FIG. 1, the boring bar, which is designated 16 in FIG. 1, is fitted through the mounting bearings 12, and the positions of the mounting bearings are adjusted relative to the mounting brackets so that the central axis of the boring bar lies on the desired central axis of the final bore. A rotational drive assembly 22 is fitted on the boring bar. The rotational drive assembly includes a clamp ring 24 that defines a cylindrical mounting cavity. When the rotational drive assembly is fitted on the boring bar, the mounting bearing 12A is received in the cylindrical mounting cavity of the clamp ring 24, and the clamp ring 24 is then tightened. In this manner, the rotational drive assembly 22 is secured to the workpiece. The spherical configuration of the external bearing surface of the mounting bearing 12A allows the clamp ring to be tightened firmly against the bearing surface even if the central axis of the boring bar does not coincide with the central axis of the mounting bearing. The rotational drive assembly includes a motor 28 that is coupled through gearing (not shown) to a drive collet 32 that is fitted on the boring bar and is keyed thereto. Thus, when power is supplied to the motor, the boring bar is driven to rotate relative to the rotational drive assembly.
An axial feed assembly 40 is also fitted on the boring bar 16. The axial feed assembly includes a housing 44 that is coupled to the rotational drive assembly through a lead screw 48 that is parallel to the boring bar and holds the housing 44 against rotation relative to the rotational drive assembly. The housing 44 contains a feed collet 52 that is rotatable within the housing 44 but is held against axial movement relative to the housing. The feed collet 52 is clamped to the boring bar 16, whereby the housing 44 is held against axial movement relative to the boring bar and the feed collet is driven to rotate inside the housing 44. The feed collet is drivingly coupled to a lead nut that is in threaded engagement with the lead screw 48. As the feed collet is rotated, the lead nut rotates and the axial feed assembly is moved toward or away from the rotational drive assembly. Thus, the boring bar is moved axially relative to the workpiece.
Proper installation of the portable boring machine is a demanding task, and it is sometimes necessary that the machine be installed in a confined space. In these circumstances, it is possible that the operator will find it difficult or inconvenient to tighten the clamp ring 24 that secures the rotational drive assembly to the mounting bearing 12A while maintaining a firm grip on the rotational drive assembly.
When the Model BB1149 Portable Boring Bar is in use, there is a possibility that the operator will not be attentive and the axial feed of the boring bar will be such that the toolhead, which is mounted on the boring bar, passes beyond the workpiece and collides with the mounting bracket or other environmental structure. This may cause damage to the boring machine or other structures.